The offshore energy industry is experiencing increasingly strict emission limits, mainly due to a continuing rise in environmental awareness. Hence, lowering emissions, fuel consumption and the overall growth of alternative power generation is a clear current, and future, development.

Sustainability is an inherent characteristic of offshore wind, and in the industry's continued search for more cost-effective and clean solutions, LNG as a marine fuel for the installation and maintenance efforts could be an interesting opportunity.

The majority of current and proposed offshore wind farms are situated in so-called ECAs (Emission Control Areas) with limits for Sulphur Oxides (SOx), Nitrous Oxides (NOx) and, Particulate Matter (PM) emissions. Liquefied Natural Gas (LNG) as a marine fuel is a solution that satisfies the limits for all emission types considered, while also offering potential fuel cost savings, compared to alternative methods. However, implementation of LNG presents several challenges; such as technical implementation, LNG supply and the optimization of the underlying business case.

Offshore wind farm installation and maintenance operations offer favorable conditions for the use of LNG. This is due to the relatively high predictability of the operational profile and proximity of shore bases and deep sea ports, which facilitates cost-effective LNG supply and minimizes the design impact on the unit.

This paper will bring together these operational, technical and commercial considerations and show how the right design approach can allow the offshore wind industry to take advantage of a fuel that is gaining traction in the maritime industry.

Method

This paper will show design approaches for two different installation units; a wind turbine installation jack-up and a foundation installation vessel. By optimizing tank arrangements and matching the LNG fuel and power generation capacity to operational and supply chain boundary conditions, cost-efficient concept designs are generated. Business cases will be investigated, taking into account a benchmark low Sulphur marine fuel and a typical cost structure for marine LNG.

Results

Results have shown that closely matching the LNG system to the operational profile yields a significant reduction in the required CAPEX. The CAPEX optimized design approach further enhances the business case for the foundation installation vessel, which has the highest decrease in fuel costs due to operations taking place in DP-mode. For the jack-up the optimization is considered essential for feasible application of LNG as marine fuel as it reduces the additional weight and keeps the payback period at a financially manageable level. Due to state of the art tank design and the design approach adopted, the weight impact for the jack-up can be as low as approx. 3-4% of the VDL.

Conclusions

The conclusions will show that feasible applications are possible when all technical, operational and economical aspects are considered at an early stage. Optimizing the LNG capacity installed to the long term average operational profile is a very effective way of reducing the CAPEX and weight impact on the design. However, the supply chain boundary conditions have to be taken into account as well. When the supply distance to the shore base increases, the delivered volume typically goes up to keep the supply case financially feasible. This might lead to buffer storages at the shore base or limit feasible application to the "larger" units that have been considered in this paper.

Objectives

Delegates will learn about LNG as a growing marine fuel and its ability to reduce fuel costs and emissions. Sustainability and innovation are staples of the offshore wind industry and cited as selection criteria throughout the value chain. LNG, when properly implemented, meets these requirements. Attendants, be they owners, operators or service providers, will learn what the feasibility conditions for LNG as a marine fuel are and how it can further enhance the cost-effectiveness and sustainability of the installation and maintenance of offshore wind farms.